Magnetic data storage media, such as magnetic tape and magnetic disks, are commonly used for storage and retrieval of data. In order to store data on a magnetic data storage medium, a recording head of a magnetic drive, such as a tape drive or disk drive, encodes the data in magnetizations of a recording layer of the medium. For example, the recording head may encode the data in transitions, which are regions of magnetization reversal. A read head of a magnetic drive may later detect the transitions, and the drive can interpret the detected transitions to retrieve the data.
Increasing data storage capacity is a paramount goal in the development of data storage media. The amount of data that a magnetic drive can store on the recording layer of a magnetic data storage medium is determined by the areal density with which bits of data are stored on the medium, and the area of the recording layer of the medium. Thus, it is desirable to increase the bit density of the medium to increase the data storage capacity for that medium without increasing the size of the medium. The drive may store bits of data on the medium end-to-end in side-by-side rows, sometimes referred to as tracks. Bit density is thus a function of length of the bits, i.e., the bit length, and the width of the tracks, i.e., the track width. In addition to increased data storage capacities, which allow storage of larger files or greater amounts of related data on a single medium, increased bit densities enable reduction in the size of magnetic data storage media and magnetic drives.
Magnetic transitions collectively represent a recorded signal that is reproduced by a magnetic drive via a read head. However, the reproduced signal typically includes noise. Generally speaking, noise comprises undesirable components of the reproduced signal that may interfere with the retrieval of the data by a magnetic drive. One type of noise that may be present in the reproduced signal is head-medium noise. Head-medium noise is caused by the interaction of the recording head and the medium surface during encoding of data on the magnetic media as transitions. Specifically, head-medium noise is caused by fluctuations in the spacing between the head and the medium surface, which are in turn caused by the interaction of the recording head with features, i.e., roughness, on the medium surface.
In order for a particular magnetic drive to accurately retrieve data stored on a magnetic data storage medium, the reproduced signal must have a sufficiently high signal-to-noise ratio. A signal-to-noise ratio is a measure of the strength of the components of a reproduced signal that communicate the data relative to the strength of the noise components of the reproduced signal. The signal-to-noise ratio of a reproduced signal typically decreases as the bit density increases. Therefore, the presence of head-medium noise in the reproduced signal limits the bit density that may be achieved on a particular magnetic data storage medium, thus limiting the data storage capacity of the medium.